The company reduced its 2014 revenue outlook to between $130 million and $140 million, down from a July estimate of between $175 million and $185 million.
Trading in Westport shares was halted pending the announcement by the company.
Westport said market uncertainty in its primary markets of Europe, Russia and China have affected revenue in its applied technologies business in the second half of this year.
As well, a change by its key development partners to move to a new high pressure direct injection system for its natural gas engines will defer related service revenue milestone payments in the near term.
Thirdly, a customer who placed a significant order for its LNG tank systems "has been unable to provide sufficient comfort to Westport that it will be able to meet its obligations and requirements in respect of such orders."
"As such Westport does not intend to ship product to this customer until such comfort has been received," the company said.
Westport also said it does not expect its combined three operating business units to report positive adjusted earnings before interest, taxes, depreciation and amoritization.
The company reiterated its goal of reporting consolidated positive adjusted EBITDA by the end of 2015.